The exemplary embodiments herein relate generally to solids-laden fluids for use in subterranean formation operations and, more particularly, to determining the concentration of solids in solids-laden fluids for use in subterranean formation operations using backscattering spectrometry.
Hydrocarbon-producing wells, be they vertical, deviated, or horizontal wells, are generally drilled using a drilling fluid pumped down a drill string and through a drill bit attached to the end of the drill string. The drilling fluid serves, among other things, to lubricate and cool the cutting surfaces of the drill bit, transport drill cuttings to the surface, control formation pressure, and maintain well stability. Various particulates may be included in a drilling fluid to influence the effectiveness of the fluid or remediate or protect the subterranean formation, such as weighting agents (e.g., barite), lubricating agents, viscosifying agents, fluid loss agents, and the like.
Once a well is in place, stimulation of the well may be achieved using hydraulic fracturing treatments. In hydraulic fracturing treatments, a viscous treatment fluid may be pumped into a portion of a subterranean formation at a rate and pressure such that the subterranean formation breaks down and one or more fractures are formed. Typically, particulate solids, such as graded sand, are introduced into the subterranean formation in a portion of the treatment fluid and deposited into the fracture. These particulate solids (generally known as “proppant particulates” or, simply, “proppant”) serve to prop the fracture open (e.g., keep the fracture from fully closing) after the hydraulic pressure is removed. By keeping the fracture from fully closing, the proppants aid in forming conductive paths through which fluids, such as hydrocarbons, may flow. Like with drilling fluids, other particulate additives may also be included in the treatment fluid to influence the effectiveness. Various particulates may be included in a drilling fluid to influence the effectiveness of the fluid or remediate or protect the subterranean formation, such as those mentioned with reference to drilling fluids, as well as other particulates such as gravel for forming a gravel pack.
The drilling fluids and treatment fluids comprising the particulate additives may be collectively referred to herein as solids-laden fluids. Such solids-laden fluids may experience a reduced solids carrying capacity, or sag, while in use in a subterranean formation or through equipment for use in performing a particular subterranean formation operation. As used herein, the term “sag” and all grammatical variants thereof refers to settling of particulate in a solids-laden fluid, including both static and dynamic conditions. The viscoelastic properties of the solids-laden fluids, exposure to shear, exposure to elevated shear rates, the geometric configuration of a wellbore (e.g., vertical or deviated), and the like, may have a significant effect on sag.
Sag may result in ineffective distribution of solids additives in the solids-laden fluid. Sag may cause the solids (e.g., weighting agents such as barite) to settle in a static or circulating solids-laden fluid in a wellbore, which may cause the upper portion of the wellbore to lose mud density, which may lessen the hydrostatic pressure and result in an influx of formation fluid. Sag may further result in failure of the solids-laden fluid to perform a particular function (e.g., failure of a fluid loss agent to reach a zone of interest or be evenly distributed in a wellbore), stuck pipe, or, in extreme cases, abandonment of a wellbore.